Thermal diffusion apparatus and method



April 17, 1956 JONES ETAL 2,742,154

THERMAL DIFFUSION APPARATUS AND METHOD Filed March 27, 1952 op BOTTOMFRACTIONS (2.2mLEAcH) FIGZ.

INVENTORS.

ARTHUR LETCHER JONES BY ERNEST C.M|LBERGER THEIR ATTORNEYS.

THERMAL DIFFUSION APPARATUS AND NIETHOD Arthur Letcher Jones, Lyndhurst,and Ernest C. iviiiberger, Maple Heights, Ohio, assignors to TheStandard Oil Company, Cleveland, Ohio, a corporation of Ohio ApplicationMarch 27, 1952, Serial No. 273,348

4 Claims. or. 210-525 The present invention relates to a liquid thermaldififusion apparatus and method that is particularly suitable forseparating small quantities of materials, such as may be desirablein'assaying the applicability of thermal dilfusion to a particularseparation. r V p The separation, by thermal diffusion, of liquidmixture, a term intended herein to include mixtures and solutions liquidunder operating conditions, into two dissimilar fractions is carried outin apparatus essentially comprising two liquid impervious walls, theopposed faces of which are smooth and spacedvsubstantially equidistantlyfrom one another to form a narrow slit, preferably having a width nogreater than about 0.15, and means are provided to maintain the opposedwalls at different temperatures to establish a temperature gradientacross the slit, one ofthe walls being referred to as the hot wall andthe other as the cold wall, the terms hot and cold being used in theirrelative rather than absolute sense. Apparatus and methods for carryingout liquid thermal diffusion on a continuous basis are described in U.SpPatents Nos. 2,541,069, 2,541,070 and 2,541,071.

It has been proposed heretofore to subject separable liquid mixtures tothermal diffusion in slits provided at the top and bottom ends with areservoir, the volume of each reservoir being relatively large ascompared with the volume ofthe slit. (Berichte, vol. 73 pages 249-269(1940).) In operation, apparatus of thistype would be filled with theliquid mixture and the opposed slit-forming wall faces would bemaintained at different temperatures to create a temperature gradientacross the slit. After many hours or several days, liquid would beremoved sepa rately from the two reservoirs and analysis would shownthem to'be enriched in one or another of the components of the liquidmixture.

Apparatus of the type heretofore proposed is extremely inefficient fromthe point of view of degree of separation obtainable in relation to thetime and heat energy consumed. It is for these reasons that earlierproposals to separate liquid mixtures by thermal diffusion remainednothing more than a laboratory curiosity for over eighty years.

The present invention is addressed particularly to static, asdistinguished from continuous, liquid thermal diffusion apparatus thatis extremely useful for separating small amounts of materials by thermaldiffusion and to assay the potentialities of the process in separatingcomponents of any particular material. In some fields, such as medicine,where only smallquantities need be separated, the apparatus and processmay be used directly in the separating V technique. The utility of theapparatus of this invention as a research tool, for example, isdemonstrated by its ability to separate components of liquid mixturesthat ice I Patented Apr. 17 1 956 rality of ports communicating with theslit, one of the ports communicating with the slit at the lo'wer endthereof and at least one other of the ports communicating with the slitat a preselected distance from the top of the slit; It

is important that there be no reservoir in communication with. the'slit,the term reservoir beingintended herein to refer to a space in whichthermal diffusion does not take place by reason of either 'or both theabsence of a temperature gradientor a width exceeding substantially thewidth of theslit. v

The width of the slit formed by the opposed walls is extremely narrow,being no greater than 0.l5' All other conditions being equal, the degreeof separation increases with a reduction in slit width, and the timerequired to reach equilibrium increases with a reduction in slit width.Hence the choice of slit width for any specific separation isnecessarily a compromise between the timeavailable, the degree ofseparation desired andthefacilities for constructing apparatus with thedesired slit width.- Inasmuch as the apparatus of: the present inventionis designed primarily for use where a high degree of separation is themain objective, the slit width ispreferablybelow about 0.015;

I The number of portscommunicating with the slit is dependent upon theseparation involved. Thus, for example, if indications are that the onlycomponent of a liquid mixture that is desired to be separated is thecomponent which accumulates in the upper fifth of the slit, then it isnecessary only to have two ports one located one-fifth the distance fromthe top of the column for removing the desired separatedcornponent, andanother at the bottom for draining the column after the desiredcomponent has been removed. Onthe other hand, where the desideratum isto find how many difierent fractions.

able means for spacing the opposed walls from one another, such as'aredisclosed in co-pending application Serial No. 271,182, filed February..12, 1952, may be utilized.

. The method of the invention comprises forming a thin, vertical film ofa-preselected quantity of the liquid mixture to be subjected to thermaldiffusion in a slit defined by smooth, liquid impervious, substantiallyequidistantly spaced wall surfaces; applying a temperature gradientacross the film until the concentrations-or compositions of dissimilarfractions at various levels of the film have reached substantialequilibrium conditions, and then removing separately the variousdissimilar frac tions.

The thickness of the vertical film should not be so great as to makenegligible the degree of separationobtainable, nor so small as toincrease unduly th time required to reach equilibrium conditions. It hasbeen found at the thickness oftlie film "should wiser searcunstsseeserased about 0115" and should preferably be do reats;

1 column such as illustrated in Figure 1.

at the bottom of the column.

his to be understood, of course, that the structure of the vent need notbe the same as or similar to that of a port. When the column is filled,one of the slit-forming walls is relatively cooled and the other isrelatively heated to produce a temperature gradient across the film of"liquid within the slit. When the temperature of the col- -umn duringoperation reaches equilibrium, it is immaterial whether the chargeportand the vent be left open or closed so long as there is no flow ofliquid mixture through the charge port. The temperature gradient acrossthe film is maintained until substantial separation,

as distinguished from temperature, equilibrium condi-- tions areobtained.

.The port immediately below the vent is then opened to drain theuppermost portion of the slit, the next lower port is then opened todrain the next lower portion of the slit, and so on, until all portionsof the slit have been separately drained.

The advantages and utility of the apparatus and method of this inventionwill become more apparent by an inner tube 11 and an outer tube 12. Theouter tube is successively wrapped with a protective covering 14,a-resistance heating wire 16, and insulating tape 17.

The inner andouter tubes 11 and 12 are suitably sealed together at thelower end 19 and at the upper end they are sealed by means of packingmaterial 20 and a packing nut 21 that allows slight relative lengthwisemovement between the tubes 11 and 12 upon being subjected to differenttemperatures. A plurality of ports 22 and a vent 23 communicating withthe slit 10, are provided along the length of the outer tube 12. Theports 22 are provided with closures located as close to the slit aspossible so that the volume of the material in the ports 22 is small.The ports 22 and the vent 23 may, for example, be of copper tubing orthe like and the closures for a port may include a fiange member 24sweated or welded onto the port, a screw cap 25 and a gasket 26.

A 50-50 mixture by volume of 2,4-dimethyl pentane and cyclohexane wassubjected to thermal diffusion in a p The annular slit has an efiectiveheight of feet, a width of 0.0115, and a volumetric capacity of 22.2 cc.Ten withdrawal ports 22 and a vent 23 are spaced six inches apart,beginning The ports 22 and the vent 23 were each constructed of /s"copper tubing having an inside diameter of approximately 0.070 and alength of about 1%". The outer tube 12 was maintainedat a temperature of105 F. by the heated resistance in Table I and are graphicallyillustrated in Figure 2 of the drawing:

Table I Charge: n 25 Cyclohexane (over 99% pure) 1.4240 2,4-dimethylpentane (over 99% pure) 1.3794 Feed (5050 mixture) 1.4018

Fraction (numbered from top) The data in the table indicate that the top30% and bottom 30% are about equal in purity to the components,represented whenpurchased as being over 99% pure, used in blending thecharge. This separation is believed to be remarkable because cyclohexaneand 2,4-dimethyl pentaue cannot be separated effectively by fractionaldistillation, their boiling points diflering by only 024 C., or bychromatographic methods.

As an additional example, catalytieally cracked residual oil boilingbetween 400 and 530 F. at 2 mm. was treated in the same apparatus. Thehot wall was maintained at a temperature of 185 F. The cold wall wasmaintained at a temperature of 70100 F. by circulating tap waterentering at 70 F. and leaving at 100 F. The

. treating time was 164 hours.

Table I I 2 Ambient Apparent 5 Temp. State Color Viscosity l. 5700Semi-Solid. Reddish-Browu.

l 54:1:0. 01 White 1 451:1:0. 001 Light Yellow. l. 4570 Yellow 1. 4650Orange Low. 1. 5000 Dark Orange. D0. 1. 6001 Medium. 1. 6552 Brown andpro- Do. 1.6704 gressively High. 1. 6821 darker brown. Do. 1. 6870 Veryhigh.

Infrared analysis of the fractions showed that the top fractioncontained almost entirely high molecular weight normal parafins and thatthe bottom fraction contained predominantly high molecular weightpolynuclear aromatic compounds such as alkyl benzanthrenes andphenanthrenes, wherein the alkyl. group was primarily methyl. Theseresults wereconfirmed by an ultra-violet analysis over a 230-450millimicron range.

From this example, the extent of the separation is readily apparent andit is possible to determine the size and operating conditions of acolumn on a commercial scale to effect any separation desired, i. e., afraction limited to the top and bottom tenth, a fraction in which thetop fifth and bottom fifth are combined, etc.

It will be readily apparent that the method and apparatus of thisinvention is applicable to the separation of many liquid mixturesthatare diflicult or incapable of separation by other methods. a

r It is also to be understood that modifications and changes to suitparticular needs will at once become apparent to those skilled in theart upon reading this description. All such modifications and changesare intended to be included within the scope of this invention asdefined in the accompanying claims.

We claim:

'1. Static liquid thermal diffusion apparatus comprising two vertical,liquid-impervious walls, the opposed faces of which are smooth andspaced substantially equidistantly and not more than 0.15 inch apart toform a narrow, vertical slit, means closing the slit at the ends thereofto confine liquid to be treated to the volume of the slit, means forrelatively heating one wall and cooling the other wall to maintain atemperature gradient across the slit, an inlet communicating with saidslit for introducing liquid to be treated into said slit, a ventcommunicating with the top of said slit, a plurality of short tubes ofsmall inside diameter communicating with the slit at vertically spacedpoints along the length of said slit, and closures for sealing saidtubes and said inlet, whereby liquid in the apparatus is confinedsubstantially completely within the slit while subjected to thermaldifiusion and a plurality of separate and distinct fractions thereof maybe withdrawn from the slit by individual removal of the closures atspaced time intervals.

2. Static liquid thermal diffusion apparatus as defined in claim 1wherein said tubes are equidistantly spaced along the length of theslit.

vall of said mixture to be separated to a thin quiescent J vertical filmnot exceeding 0.015 inch thick, applying a References Cited in the fileof this patent UNITED STATES PATENTS 2,158,238 Hvid May 16, 19392,521,112 7 Beams Sept. 5, 1950 2,541,070 Jones et al Feb. 13, 19512,585,244 Hanson Feb. 12, 1952 7 OTHER REFERENCES Deutsche ChemischeGesellschaft, vol. 73 (1940), pages 249-269. V

temperature gradient across said film until the concentrations ofdissimilar fractions at various levels thereof have reached substantialequilibrium conditions, and then removing separately the variousdissimilar fractions at a plurality of levels spaced "vertically alongsaid film, said fractions being removed in succession from top to bottomof said film.

4. Static liquid thermal difiusion apparatus comprising two vertical,liquid-impervious walls, the opposed faces of which are smooth andspaced less than about 0.015" from one another to form a narrow,substantially uniform vertical slit, means closing the slit at the endsthereof to confine liquid to be treated to the volume of the slit, meansfor relatively heating one wall and cooling the other Wall to maintain atemperature gradient across the slit, an inlet for filling said slitwith liquid, a vent communicating with the top of said slit and aplurality of short tubes of small inside diameter communicating with theslit, 'one of said tubes communicating with the slit near the lower endthereof and at least one of said tubes communicating with the slit at apreselected distance from the top of the slit.

1. STATIC LIQUID THERMAL DIFFUSION APPARATUS COMPRISING TWO VERTICAL,LIQUID-IMPERVIOUS WALLS, THE OPPOSED FACES OF WHICH ARE SMOOTH ANDSPACED SUBSTANTIALLY EQUIDISTANTLY AND NOT MORE THAN 0.15 INCH APART TOFORM A NARROW, VERTICAL SLIT, MEANS CLOSING THE SLIT AT THE ENDS THEREOFTO CONFINE LIQUID TO BE TREATED TO THE VOLUME OF THE SLIT, MEANS FORRELATIVELY HEATING ONE WALL AND COOLING THE OTHER WALL TO MAINTAIN ATEMPERATURE GRADIENT ACROSS THE SLIT, AN INLET COMMUNICATING WITH SAIDSLIT FOR INTRODUCING LIQUID TO BE TREATED INTO SAID SLIT, A VENTCOMMUNICATING WITH THE TOP OF SAID SLIT, A PLURALITY OF SHORT